This Phase II SBIR application proposes research that builds on a novel, solid phase, colorimetric immunoassay system for the quantitative measurement of progesterone in milk of cows, the feasibility of which was shown during Phase I research. A good correlation between concentrations of progesterone in milk measure by a conventional method using radiolabeled tracer and the newly developed enzyme immunoassay has been obtained. The assay system is based on use of monoclonal antibodies that are covalently linked by a proprietary method to microplate wells in combination with a non-radioactive, enzyme-based signal generator. Phase II research will be aimed at developing the assay into a simple, reliable system for monitoring the estrous cycle, ovarian cyclicity post partum, ovarian dysfunction, and pregnancy in dairy cows which can be performed under field conditions by a non-trained person. The envisioned system is one that will be easy to use, will not require extraction or chromatography, and will give rapid, quantitative results. Quantitation will be accomplished with a manual colorimeter that can be coupled directly to a computer running custom software. The system will be built upon a novel device (patient pending) that serves to collect and process fluids automatically yielding in a few minutes several milliliters of clear, protein-free filtrate containing compounds of low molecular weight. During Phase II, an integrated approach designed to simplify the manner that the assay is run will be developed, the assay will be made robust for use in the field, further validation for the thus modified assay will be sought, its usefulness in a dairy barn will be demonstrated, and prototype systems able to attract phase III support for commercialization will be developed.